Tubular metal webs with thin flat ends have been used for constructing wood chord trusses for such a long time and in such great quantity that they have become an unquestioned standard in the truss industry. The flat thin ends, however, pose a nagging problem; under compression, the webs buckle at a small fraction of the load the webs are capable of withstanding in tension.
Troutner, U.S. Pat. No. 3,137,899, June 22, 1964 was one of the earliest to use a tubular metal web with thin flat ends in his composite wood chord light truss. The thin flat end web was an easy choice since such webs with thin flat ends had been used since the early thirties in all-metal light trusses as shown e.g. in Wooldrige, U.S. Pat. No. 1,813,373, July 7, 1931. Troutner was soon followed by Birkemier U.S. Pat. No. 3,570,204, Mar. 16, 1971; Peters, U.S. Pat. No. 3,961,455, June 8, 1976 and Gilb, U.S. Pat. No. 3,857,218, Dec. 31, 1974; all using the tubular web with the thin flat ends.
Web buckling was not a serious problem in light composite trusses since all of the trusses except the Gilb trusses, failed at maximum load at the interface of the metal pin and the wood chord by chord splitting.
Web failure became an acute problem, however, in the medium and heavy truss series which used four wood chords. Troutner, U.S. Pat. No. 3,386,222 tried to solve the web buckling problem at the thin flat ends by forming diagonal asymmetrical shoulders in the web ends. Even though the Troutner web still did not basically solve the buckling problem, because it still was constructed with a long thin flat area adjacent the pin opening, it was apparently sufficient for the Troutner truss with its basic metal pin and bored wood chord joint.
In 1976, however, the Gilb U.S. Pat. No. 3,946,532, Mar. 30, 1976, Truss Structure With Fastener Plate Joint Assembly made a quantum jump in medium and heavy truss joint load values. The Gilb prong plates with metal to metal contact suddenly made metal compression webs with thin flat ends obsolete. Further increases in load value for medium and heavy series trusses awaited the invention of a stronger compression web.
Finally, while working on a different project to improve the light series truss line, Gilb invented a new truss joint connector which has been named the "clevis". The "clevis" truss had such high load value at the joints that even oversized webs with the standard thin flat ends were unable to meet the high loads imposed. Gilb filed application Ser. No. 758,061 on Jan. 10, 1977 on the clevis assembly joint. Buckling failures in the thin flat ends of the webs had to be solved or the development of higher load value connectors for the light-weight series of composite trusses would be at a standstill.